Molecular Weight-Independent "Polysoap" Nanostructure Characterized via In Situ Resonant Soft X-ray Scattering.

Studying polymer micelle structure and loading dynamics under environmental conditions is critical for nanocarrier applications but challenging due to a lack of in situ nanoprobes. Here, the structure and loading of amphiphilic polyelectrolyte copolymer micelles, formed by 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and n-dodecyl acrylamide (DDAM), were investigated using a multimodal approach centered around in situ resonant soft X-ray scattering (RSoXS). We observe aqueous micelles formed from polymers of wide-ranging molecular weights and aqueous concentrations. Despite no measurable critical micelle concentration (CMC), structural analyses point toward multimeric structures for most molecular weights, with the lowest molecular weight micelles containing mixed coronas and forming loose micelle clusters that enhance hydrocarbon uptake. The sizes of the micelle substructures are independent of both the concentration and molecular weight. Combining these results with a measured molecular weight-invariant surface charge and zeta potential strengthens the link between the nanoparticle size and ionic charge in solution that governs the polysoap micelle structure. Such control would be critical for nanocarrier applications, such as drug delivery and water remediation.

High Sensitivity of Non-Fullerene Organic Solar Cells Morphology and Performance to a Processing Additive.

Although solvent additives are used to optimize device performance in many novel non-fullerene acceptor (NFA) organic solar cells (OSCs), the effect of processing additives on OSC structures and functionalities can be difficult to predict. Here, two polymer-NFA OSCs with highly sensitive device performance and morphology to the most prevalent solvent additive chloronaphthalene (CN) are presented. Devices with 1% CN additive are found to nearly double device efficiencies to 10%. However, additive concentrations even slightly above optimum significantly hinder device performance due to formation of undesirable morphologies. A comprehensive analysis of device nanostructure shows that CN is critical to increasing crystallinity and optimizing phase separation up to the optimal concentration for suppressing charge recombination and maximizing performance. Here, domain purity and crystallinity are highly correlated with photocurrent and fill factors. However, this effect is in competition with uncontrolled crystallization of NFAs that occur at CN concentrations slightly above optimal. This study highlights how slight variations of solvent additives can impart detrimental effects to morphology and device performance of NFA OSCs. Therefore, successful scale-up processing of NFA-based OSCs will require extreme formulation control, a tuned NFA structure that resists runaway crystallization, or alternative methods such as additive-free fabrication.

Evidence That Sharp Interfaces Suppress Recombination in Thick Organic Solar Cells.

Commercialization and scale-up of organic solar cells (OSCs) using industrial solution printing require maintaining maximum performance at active-layer thicknesses >400 nm─a characteristic still not generally achieved in non-fullerene acceptor OSCs. NT812/PC71BM is a rare system, whose performance increases up to these thicknesses due to highly suppressed charge recombination relative to the classic Langevin model. The suppression in this system, however, uniquely depends on device processing, pointing toward the role of nanomorphology. We investigate the morphological origins of this suppressed recombination by combining results from a suite of X-ray techniques. We are surprised to find that while all investigated devices are composed of pure, similarly aggregated nanodomains, Langevin reduction factors can still be tuned from ∼2 to >1000. This indicates that pure aggregated phases are insufficient for non-Langevin (reduced) recombination. Instead, we find that large well-ordered conduits and, in particular, sharp interfaces between domains appear to help to keep opposite charges separated and percolation pathways clear for enhanced charge collection in thick active layers. To our knowledge, this is the first quantitative study to isolate the donor/acceptor interfacial width correlated with non-Langevin charge recombination. This new structure-property relationship will be key to successful commercialization of printed OSCs at scale.

Label-free characterization of organic nanocarriers reveals persistent single molecule cores for hydrocarbon sequestration.

Self-assembled molecular nanostructures embody an enormous potential for new technologies, therapeutics, and understanding of molecular biofunctions. Their structure and function are dependent on local environments, necessitating in-situ/operando investigations for the biggest leaps in discovery and design. However, the most advanced of such investigations involve laborious labeling methods that can disrupt behavior or are not fast enough to capture stimuli-responsive phenomena. We utilize X-rays resonant with molecular bonds to demonstrate an in-situ nanoprobe that eliminates the need for labels and enables data collection times within seconds. Our analytical spectral model quantifies the structure, molecular composition, and dynamics of a copolymer micelle drug delivery platform using resonant soft X-rays. We additionally apply this technique to a hydrocarbon sequestrating polysoap micelle and discover that the critical organic-capturing domain does not coalesce upon aggregation but retains distinct single-molecule cores. This characteristic promotes its efficiency of hydrocarbon sequestration for applications like oil spill remediation and drug delivery. Such a technique enables operando, chemically sensitive investigations of any aqueous molecular nanostructure, label-free.

Evidence for Field-Dependent Charge Separation Caused by Mixed Phases in Polymer-Fullerene Organic Solar Cells.

As organic photovoltaic performance approaches 20% efficiencies, causal structure-performance relationships must be established for devices to realize theoretical limits and become commercially competitive. Here, we reveal evidence of a causal relationship between mixed donor-acceptor interfaces and charge generation in polymer-fullerene solar cells. To do this, we combine a holistic loss analysis of device performance with quantitative synchrotron X-ray nanocharacterization to identify a >98% anticorrelation between field-dependent geminate recombination and nanodomain purity. Importantly, our analysis eliminates other possible explanations of the performance trends, a requirement to establish causality. The unprecedented granular level of our analysis also separates field-dependent and field-independent recombination at the interface, where we find for the first time that this system is free of field-independent recombination, a loss channel that plagues high-performance systems, including those with non-fullerene acceptors. This result broadens the case that minimizing mixed phases to promote sharp interfaces between pure aggregated domains is the ideal nanostructure for realizing theoretical efficiency limits of organic photovoltaics.

A NIST facility for resonant soft x-ray scattering measuring nano-scale soft matter structure at NSLS-II.

We present the design and performance of a polarized resonant soft x-ray scattering (RSoXS) station for soft matter characterization built by the national institute of standards and technology at the national synchrotron light source-II (NSLS-II). The RSoXS station is located within the spectroscopy soft and tender beamline suite at NSLS-II located in Brookhaven national laboratory, New York. Numerous elements of the RSoXS station were designed for optimal performance for measurements on soft matter systems, where it is of critical importance to minimize beam damage and maximize collection efficiency of polarized x-rays. These elements include a novel optical design, sample manipulator and sample environments, as well as detector setups. Finally, we will report the performance of the measurement station, including energy resolution, higher harmonic content and suppression methods, the extent and mitigation of the carbon absorption dip on optics, and the range of polarizations available from the elliptically polarized undulator source.

The role of socioeconomic and sociocultural predictors of Spanish and English proficiencies of young Latino children of immigrants.

Young Latino children of immigrants typically speak primarily Spanish at home and are exposed to varying amounts of English. As a result, they often enter school with a wide range of proficiencies in each language. The current study investigated family background, language use at home and early childhood settings as predictors of Spanish and English language proficiencies among Latino dual language children (N = 228). Findings demonstrated divergent sets of predictors were associated with either Spanish or English proficiencies at kindergarten and second grade. Sociocultural variables (parent origin, gender, home language use, home literacy practices, and language use in early childhood settings) predicted children's Spanish proficiency, while socioeconomic variables (poverty, and maternal and paternal education) predicted children's English proficiency, with little to no overlap in these predictions. These results suggest that different supports are required for proficiency in Spanish and in English, highlighting the importance of sociocultural and socioeconomic factors.

Probing the pathways of free charge generation in organic bulk heterojunction solar cells.

The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges.

Quantitative relations between interaction parameter, miscibility and function in organic solar cells.

Although it is known that molecular interactions govern morphology formation and purity of mixed domains of conjugated polymer donors and small-molecule acceptors, and thus largely control the achievable performance of organic solar cells, quantifying interaction-function relations has remained elusive. Here, we first determine the temperature-dependent effective amorphous-amorphous interaction parameter, χaa(T), by mapping out the phase diagram of a model amorphous polymer:fullerene material system. We then establish a quantitative 'constant-kink-saturation' relation between χaa and the fill factor in organic solar cells that is verified in detail in a model system and delineated across numerous high- and low-performing materials systems, including fullerene and non-fullerene acceptors. Our experimental and computational data reveal that a high fill factor is obtained only when χaa is large enough to lead to strong phase separation. Our work outlines a basis for using various miscibility tests and future simulation methods that will significantly reduce or eliminate trial-and-error approaches to material synthesis and device fabrication of functional semiconducting blends and organic blends in general.

Spectral Analysis for Resonant Soft X-Ray Scattering Enables Measurement of Interfacial Width in 3D Organic Nanostructures.

Interfaces are of critical importance to many materials and phenomena yet are difficult to probe. This difficulty is compounded in three-dimensional nanostructures and with delicate organic materials. Here we demonstrate a quantitative spectral analysis of resonant soft x-ray scattering that can accurately measure properties of buried nonplanar interfaces within polymeric systems. We measure the scattering invariant on an absolute scale to quantify the interfacial volume and width involved in mixing at the interface of block copolymer nanostructures. Using continuous contrast tuning, this spectral analysis enables the separation and identification of any number of unique scatterers in complex nanostructures.

Structural control of mixed ionic and electronic transport in conducting polymers.

Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT: PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT: PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT: PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. These findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.

Origins of polarization-dependent anisotropic X-ray scattering from organic thin films.

Organic thin films that have no overall in-plane directional ordering often nonetheless produce anisotropic scattering patterns that rotate with the polarization of incident resonant X-rays. Isotropic symmetry is broken by local correlations between molecular orientation and domain structure. Such examples of molecular alignment at domain interfaces and within the bulk of domains, which are both critical to fields such as organic electronics, are simulated and compared with experimental scattering. Anisotropic scattering patterns are found to allow unambiguous identification of the mechanism of local molecular orientation correlations and, as such, promise to be both distinct and complementary to isotropic scattering intensity as a general measure of thin film microstructure.

Does a prophylactic dose of propofol reduce emergence agitation in children receiving anesthesia? A systematic review and meta-analysis.

INTRODUCTION: Emergence agitation (EA) is common after sevoflurane anesthesia in children, and can lead to distressing inconsolability, agitation, crying, and injury. Use of a single dose of the short-acting sedative-hypnotic agent propofol at the end of a procedure has shown promise for preventing EA, but evidence evaluating the efficacy and safety of this approach has not been formally summarized. OBJECTIVE: The objective of this review was to assess the effects of a prophylactic dose of propofol vs placebo on the incidence and severity of EA in children age 0-13 years receiving general inhalational anesthesia. SEARCH METHODS: We searched PubMed (1946-2013) via Medline, CENTRAL (1898-2013), and Web of Science (1900-2013) without limits or language restrictions; we also searched ClinicalTrials.gov and reference lists. We reviewed abstracts from the 2012 and 2013 Society for Pediatric Anesthesia meetings and pediatric anesthesia-related abstracts from the 2012 and 2013 International Anesthesia Research Society meetings. SELECTION CRITERIA: We assessed randomized, double-blind trials evaluating the efficacy of a prophylactic dose of propofol (1 mg·kg(-1) ) vs placebo given at the end of inhalational anesthesia to prevent EA in pediatric patients. Studies were required to follow patients through recovery and report at least one prespecified outcome. DATA COLLECTION AND ANALYSIS: Two authors independently assessed trial quality and extracted data from included studies. We contacted study authors regarding any missing data. We used the random effects models to calculate pooled relative risks (RR) and weighted mean differences (WMD). We collected Pediatric Anesthesia Emergence Delirium (PAED) scale scores from included studies. PAED scale scores can range from 0 to 20. MAIN RESULTS: Of 276 studies screened, nine trials involving 997 children met all inclusion criteria. All were considered low risk of bias. For one non-English trial, we obtained a full-text translation and for one non-English trial, we used the English-language abstract, tables, and figures. Based on available evidence, prophylactic propofol was associated with both decreased incidence of EA (29% vs 58%, RR 0.50, 95% confidence intervals [CI] 0.41, 0.61, I(2) = 37%, seven studies), and reduced severity of EA as assessed by mean PAED scale score (WMD -2.08 points, 95% CI -3.20, -0.96, I(2) = 0%, three studies), when compared to placebo. In addition, though prophylactic propofol did lengthen the time to awakening (WMD 4.07 min, 95% CI 2.22, 5.91, I(2) = 82%, six studies), it did not increase recovery time (WMD 2.91 min, 95% CI -0.59, 6.41, I(2) = 82%, six studies) when compared to placebo. No significant adverse events were reported in either arm. CONCLUSION: Based on high quality evidence, prophylactic propofol appears to be effective for reducing the incidence and severity of EA in children emerging from general anesthesia.

Dual Language Development of Latino Children: Effect of Instructional Program Type and the Home and School Language Environment.

Latino dual language children typically enter school with a wide range of proficiencies in Spanish and English, many with low proficiency in both languages, yet do make gains in one or both languages during their first school years. Dual language development is associated with how language is used at home and school, as well as the type of instructional program children receive at school. The present study investigates how changes in both Spanish and English proficiencies of Latino, second-generation immigrant children (n =163) from kindergarten to second grade relate to instructional program type as well as language use at home and school. A series of MANCOVAs demonstrated significant dual language gains in children who were in bilingual classrooms and schools where Spanish was used among the teachers, students, and staff. Furthermore, only in classrooms where both Spanish and English were used did children reach age-appropriate levels of academic proficiency in both languages. Home language use was also significantly associated with dual language gains as was maternal Spanish vocabulary knowledge before controlling for maternal education. Educational implications and potential benefits associated with bilingualism are discussed.

Dual language profiles of Latino children of immigrants: Stability and change over the early school years.

Dual language children enter school with varying levels of proficiencies in their first and second language. This study of Latino children of immigrants (N = 163) analyzes their dual language profiles at kindergarten and second grade, derived from the direct assessment of Spanish and English proficiencies (Woodcock Language Proficiency Batteries-Revised). Children were grouped based on the similarity of language profiles (competent profiles, such as dual proficient, Spanish proficient, and English proficient; and low-performing profiles, including borderline proficient and limited proficient). At kindergarten, the majority of children (63%) demonstrated a low-performing profile; by second grade, however, the majority of children (64%) had competent profiles. Change and stability of language profiles over time of individual children were then analyzed. Of concern, are children who continued to demonstrate a low-performing, high-risk profile. Factors in the linguistic environments at school and home, as well as other family and child factors associated with dual language profiles and change/stability over time were examined, with a particular focus on the persistently low-performing profile groups.

The role of regioregularity, crystallinity, and chain orientation on electron transport in a high-mobility n-type copolymer.

We investigated the correlation between the polymer backbone structural regularity and the charge transport properties of poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} [P(NDI2OD-T2)], a widely studied semiconducting polymer exhibiting high electron mobility and an unconventional micromorphology. To understand the influence of the chemical structure and crystal packing of conventional regioregular P(NDI2OD-T2) [RR-P(NDI2OD-T2)] on the charge transport, the corresponding regioirregular polymer RI-P(NDI2OD-T2) was synthesized. By combining optical, X-ray, and transmission electron microscopy data, we quantitatively characterized the aggregation, crystallization, and backbone orientation of all of the polymer films, which were then correlated to the electron mobilities in electron-only diodes. By carefully selecting the preparation conditions, we were able to obtain RR-P(NDI2OD-T2) films with similar crystalline structure along the three crystallographic axes but with different orientations of the polymer chains with respect to the substrate surface. RI-P(NDI2OD-T2), though exhibiting a rather similar LUMO structure and energy compared with the regioregular counterpart, displayed a very different packing structure characterized by the formation of ordered stacks along the lamellar direction without detectible π-stacking. Vertical electron mobilities were extracted from the space-charge-limited currents in unipolar devices. We demonstrate the anisotropy of the charge transport along the different crystallographic directions and how the mobility depends on π-stacking but is insensitive to the degree or coherence of lamellar stacking. The comparison between the regioregular and regioirregular polymers also shows how the use of large planar functional groups leads to improved charge transport, with mobilities that are less affected by chemical and structural disorder with respect to classic semicrystalline polymers such as poly(3-hexylthiophene).

Fullerene-Free Polymer Solar Cells with Highly Reduced Bimolecular Recombination and Field-Independent Charge Carrier Generation.

Photogeneration, recombination, and transport of free charge carriers in all-polymer bulk heterojunction solar cells incorporating poly(3-hexylthiophene) (P3HT) as donor and poly([N,N'-bis(2-octyldodecyl)-naphthelene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as acceptor polymer have been investigated by the use of time delayed collection field (TDCF) and time-of-flight (TOF) measurements. Depending on the preparation procedure used to dry the active layers, these solar cells comprise high fill factors (FFs) of up to 67%. A strongly reduced bimolecular recombination (BMR), as well as a field-independent free charge carrier generation are observed, features that are common to high performance fullerene-based solar cells. Resonant soft X-ray measurements (R-SoXS) and photoluminescence quenching experiments (PQE) reveal that the BMR is related to domain purity. Our results elucidate the similarities of this polymeric acceptor with the superior recombination properties of fullerene acceptors.

Modifications in morphology resulting from nanoimprinting bulk heterojunction blends for light trapping organic solar cell designs.

Nanoimprinting the photoactive layer of bulk heterojunction (BHJ) organic solar cells is a promising technique for enhancing device performance via improved light absorption. Here, we demonstrate that imprinting poly(3-hexylthiophene) (P3HT) and fullerene BHJ blends leads to adverse morphological changes within the photoactive nanopattern which have been previously overlooked. In particular, nanoimprinting induces a factor of 2 difference in polymer:fullerene composition between the nanopattern posts and interconnecting flash layer that inadvertently moves the composition outside the range for optimal performance. This occurs because of the strong tendency of regioregular P3HT to crystallize since imprinting blends based on amorphous regiorandom P3HT have uniform nanopattern composition. Based on these results, we outline promising design strategies, such as nanoimprinting amorphous polymers, to serve as guidelines for fabricating high-performance nanopatterned BHJ solar cells capable of maximized light absorption.

Cross-Sectional Study of Unmet Mental Health Need in 5- to 7-Year Old Latino Children in the United States: Do Teachers and Parents Make a Difference in Service Utilization?

The aim of the study is to examine the rates of mental health service utilization in young Latino children of immigrants in relation to maternal and teacher reports of child mental health need. Specific knowledge is lacking about gaps in service utilization among young Latino children, the fastest growing and possibly the most underserved segment of the US child population. The associations of mental health service utilization (Service Assessment for Children and Adolescents) and mental health need (clinical levels of internalizing, externalizing, or total problems reported by mothers [Child Behavior Checklist] and teachers [Teacher's Report Form]) were examined in a community sample of young Latino children of immigrants (n = 228; mean age = 6) and compared across mothers' and teachers' responses. Mother-teacher agreement was also studied. Sixty-five children (28.5 %) had a mental health need; most (76.9 %) of these received no services. For all types of mental health need, service utilization was more likely when need was reported by mothers rather than teachers (p = .03). Teachers' reports were not associated with service utilization. Mother-teacher agreement was low for externalizing (r = .23; p ≤ 0.01) and total problems (r = .21; p ≤ 0.05), and nonsignificant for internalizing problems. This study is the first in the United States to document, in such a young Latino group, high rates of unmet need comparable to those among older Latino youth; low or no mother-teacher agreement on which children had a mental health need; low utilization of school-based services; and a lack of association between service utilization and teacher-reported mental health need-both for externalizing and internalizing problems. These findings suggest that schools are not effectively leveraging mental health services for young Latino children. Potential factors responsible for the findings are discussed.

Behavior problems in late childhood: the roles of early maternal attachment and teacher-child relationship trajectories.

The purposes of the current study were: (1) to examine the roles of early maternal attachment relationships and teacher-child relationships during childhood for externalizing and internalizing behaviors in late childhood, and (2) to investigate teacher-child relationships, as well as externalizing and internalizing behaviors in early childhood as possible mechanisms linking early maternal attachment relationships to behavior problems in late childhood. Longitudinal data from the National Institute of Child Health and Human Development Early Child Care Research Network Study of Early Child Care and Youth Development (N = 1140 mothers and children) were used in this investigation. There were three main findings. First, insecure/other maternal attachment relationships in early childhood (i.e., 36 months) were associated with externalizing and internalizing behaviors in late childhood (Grade 5). Second, elevated levels of teacher-child conflict during childhood were associated with externalizing behaviors in late childhood whereas low levels of teacher-child closeness were associated with internalizing behaviors. Third, the effects of insecure/other attachment on externalizing and internalizing behaviors in late childhood were mediated through teacher-child relationships during childhood and early externalizing and internalizing behaviors. Implications for attachment theory are discussed.